Quasimodo personifies the concept that you shouldn't judge a person by their outward appearance. Quasimondo is described as so ugly that people call him a "creation of the devil." He has a hunched back and a disfiguring wart over one eye. Becoming the bellringer at Notre Dame Cathedral in Paris leaves him deaf. He is also of Roma descent, part of a despised group that is considered criminal and deviant by much of the rest of society.
Abandoned in infancy, Quasimodo, like Frankenstein's creature, longs for the love that he is denied because people find him so hideous that they assume he is evil. He is a figure of deep pathos, as he has a good and compassionate heart and merely wants what ordinary people have, which is a little love. He is so needy for love that he allows the evil Frollo, who he thinks loves him, to manipulate him into doing evil acts, such as attempting to kidnap Esmeralda.
Quasimodo falls truly in love with the one person who is genuinely kind to him, Esmeralda, and does what he can to save to her, saying of her, "There is all that I ever loved!"
We feel for Quasimodo despite his appearance, because he has endured a harsh, cruel life and loses the one person he cared for and who cares for him. He is a Romantic character, alone and abandoned by a society that doesn't understand him.